1. Field of the Invention
The present invention relates generally to downhole oil well tools run on a pipe string, such as impact, drilling, or jarring type downhole oil well tools, and more particularly, to a fluid operated tool for use in well bores wherein an anti-chatter switch prevents valve chatter when running into the well bore.
2. General Background of the Invention
In downhole well operations, there is often a need for jarring or impact devices. For example, in work over operations using a pipe string such as coil tubing or snubbing equipment, it is necessary to provide downward jarring impact at the bottom of the string to enable the string to pass obstructions or otherwise enter the well. During fishing operations or other operations, such as opening restriction (i.e., collapsed tubing) it is sometimes necessary to apply upward jarring or impact forces at the bottom of the string if the fishing tool or the like becomes stuck.
In prior U.S. Pat. No. 3,946,819, naming the applicant herein as patentee, there is disclosed a fluid operated well tool adapted to deliver downward jarring forces when the tool encounters obstructions. The tool of my prior U.S. Pat. No. 3,946,819, generally includes a housing with a tubular stem member telescopically received in the housing for relative reciprocal movement between a first terminal position and a second terminal position in response to fluid pressure in the housing. The lower portion of the housing is formed to define a downwardly facing hammer and the stem member includes an upwardly facing anvil which is positioned to be struck by the hammer. The tool includes a valve assembly that is responsive to predetermined movement of the stem member toward the second terminal position to relieve fluid pressure and permit the stem member to return to the first terminal position. When the valve assembly relieves fluid pressure, the hammer moves into abrupt striking contact with the anvil. The tool of prior U.S. Pat. No. 3,946,819, is effective in providing downward repetitive blows. The tool of the '819 patent will not produce upwardly directed blows.
In prior U.S. Pat. No. 4,462,471, naming the applicant herein as patentee, there is provided a bidirectional fluid operated jarring apparatus that produces jarring forces in either the upward or downward direction. The jarring apparatus was used to provide upward or downward impact forces as desired downhole without removing the tool from the well bore for modification. The device provides downward jarring forces when the tool is in compression, as when pipe weight is being applied downwardly on the tool, and produces strong upward forces when is in tension, as when the tool is being pulled upwardly.
In U.S. Pat. No. 4,462,471, there is disclosed a jarring or drilling mechanism that may be adapted to provide upward and downward blows. The mechanism of the '471 patent includes a housing having opposed axially spaced apart hammer surfaces slidingly mounted within the housing between the anvil surfaces. A spring is provided for urging the hammer upwardly. When it is desired to use the mechanism of the '471 patent for jarring, a valve including a closure and a compression spring is dropped down the string to the mechanism.
In general, the mechanism of the '471 patent operates by fluid pressure acting on the valve and hammer to urge the valve and hammer axially downwardly until the dowvnward movement of the valve is stopped, preferably by the full compression of the valve spring. When the downwvard movement of the valve stops, the seal between the valve and the hammer is broken and the valve moves axially upwardly.
The direction jarring of the mechanism of the '471 patent is determined by the relationship between the fluid pressure and the strength of the spring that urges the hammer upwardly. Normally, the mechanism is adapted for upward jarring. When the valve opens, the hammer moves upwardly to strike the downwardly facing anvil surface of the housing.
U.S. Pat. No. 5,156,223 discloses a fluid operated vibratory jar with rotating bit that uses impact, reciprocal drilling and an improved rotating bit or working member. That apparatus includes the receipt of both fluid pressure and weight from an elongated pipe string with a flow bore in order to drive the tool. A valve within the tool housing controls fluid pressure to the working end so that the tool pressures up, then releases pressure through the working member allowing the pipe string to load the bit, creating impact. A clutch is disclosed in the '223 patent that rotates the working member during drilling to prevent imprint upon the formation. A bias spring is provided to control and adjust the amount of weight on the bit independent of pipe weight. U.S. Pat. No. 5,156,223 is incorporated herein by reference.
When the prior tool of U.S. Pat. No. 5,516,223 is lowered into the well, it is neither in tension nor compression. But as the springs that deliver the energy for the upward blow are preloaded (compressed) between the piston and the housing during assembly, the piston is predetermined to rest at the top of its stroke.
The normal resting for the dart valving member places it very close to the seat. Therefore, any fluid pumped through the tool pulls the valving member on to the seat. The piston then begins to move down due to pressure build up in chamber. The piston pulls the dart valving member down with it as they are locked together by differential pressure across the seat.
As the dart valving member moves downward, it compresses the spring. When the upward forces building in the spring become greater than the force holding valving member to valve seat, the seal is broken. The dart valving member moves upward and the piston follows closely urged by the spring. The cycle begins again, resulting in chatter and seat wear.